The biosolid method is now widely practiced for cleaning of waste water. The biosolid method is a method in which a biochemical treatment is undertaken by utilizing microorganisms and oxygen so as to immobilize organic pollutant substances in the waste water as bio-solid which is partly decomposed to form water and carbon dioxide (self-digestion) to be removed.
In a standard biosolid method, non-organic matters such as coarse suspended substances, sand and the like are removed, in a settling vessel (also called a settling pool) from the original waste water introduced into the waste water treatment system and the organic matters are decomposed by means of microorganisms in a reaction vessel under an anaerobic atmosphere (sometimes called an anaerobic vessel) to be converted into water-soluble substances and a biochemical reaction is conducted by means of microorganisms in a reaction vessel under an aerobic atmosphere (sometimes called an aeration vessel or aerobic vessel) followed by settling of the biosolid produced in the reaction vessel, in a biosolid settling vessel (also called a biosolid settling pool) and release of the supernatant water from the waste water treatment system along with recycling of a part of the biosolid into the reaction vessel and elsewhere as the recycled biosolid for recycling utilization of the microorganisms while the remainder of the biosolid as the excessive biosolid is, after treatments of dehydration, drying and the like, disposed by compost-forming or incineration or disposed by land filling.
The supernatant water is released to rivers and the like or subjected to an advanced treatment for further purification.
While, in many cases, the reaction vessel, biosolid settling vessel and others are installed each as an independent vessel (pool) (represented by “vessel” hereinafter) for an exclusive purpose, it is sometimes the case that a vessel is provided to exhibit functions of a plurality thereof in combination and that a single vessel is provided for utilization in a batch-wise manner. Also, there can be a case where vessels of other kinds such as, for example, an adjustment vessel and others are provided. In order to conduct the biochemical reaction by means of the aerobic microorganisms in the reaction vessel (aerobic) under an aerobic atmosphere, the dissolved oxygen is indispensable in the water under disposal.
In the reaction vessel (aerobic), it was the case that air was introduced by using an air disperser unit (bubbling) in order to promote the biochemical reaction. The utilization efficiency of oxygen, however, was very low because the diameter of the gas bubbles introduced into the disposal water by the air disperser unit was very large so that most part of the gas rapidly ascended in the disposal water to be dissipated from the water surface. Accordingly, there are means under practice in which aeration with standard air is replaced by aeration with oxygen-enriched air or pure oxygen, a great increase of the aeration volume is attempted and the depth of the vessel is increased to make efficient the water depth pressure thereby only to result in an increase of the power consumption or necessity of an excessive space for the reaction vessel.
On the other hand, the present status for the disposal of the excessive biosolid occurring in a large amount in the biosolid method is as follows.                1) A part is converted into compost.        2) A wet-process oxidative annihilation treatment is undertaken in part under a pressure of 4.99 MPa (50 kg/cm2) or higher at a temperature of 243° C. or higher.        3) A biogas recovery method by biosolid digestion is now under way of development.        
It is, however, the usual case that the excessive biosolid is disposed by concentration, carrying-out, incineration and land filling and the disposal cost, bad smells, CO2 emission and others belong to the fatal problems of the biosolid method and fundamental solutions remain unpracticed in the present status.
As a measure for volume reduction of the excessive biosolid, practice is also under way for the application of gaseous ozone to a waste water treatment system by the biosolid method (official publication of Patent Publication No. 5-85236, official publication of Patent Ko-kai No. 6-206088, official publication of Patent Publication No. 57-19719 and elsewhere).
According to the official publication of Patent Publication No. 5-85236, the disclosures given include that “the microorganisms are activated by ozone simultaneously with the deodorizing activity and oleaginous matter decomposing activity” to be exhibited and, besides, “according to the present invention, the organic substances contained in the waste water are decomposed mainly to carbon dioxide and water so that occurrence of biosolid can be prevented”.
According to the official publication of Patent Kokai No. 6-206088, a disclosure is given that “when reacted with an ozone-containing gas, the extracted biosolid is converted into BOD by causing oxidative decomposition”.
According to the official publication of Patent Publication No. 57-19719, the disclosure says: “When the biosolid is contacted with ozone, the organic matters in the suspended substances constituting the bio-solid are decomposed by the organic-decomposing activity of ozone leading to the formation of another biosolid of which the constituents are different from those in the biosolid before contacting with ozone. When this biosolid is added to the reaction vessel, the living organisms in the vessel take up the same as the nutrient source so that the suspended substances having a decreased molecular size by ozone are decomposed to result in a decrease of the SS.”
Contacting of an ozone-containing gas with the disposal water in these prior art technologies is undertaken always by using the means of bubbling in the same manner as in the aforementioned oxygen gas. It is therefore that the size of the bubbles of the ozone-containing gas is about 1 mm or in the order of submillimeter for the smallest so that the dissolving rate of ozone into water is so low that the dissolution and utilization efficiency would presumably be low.
The above-described prior art technologies always involve the step of oxygen aeration with oxygen gas or an ozone-containing gas as a hardly dissolvable gas and always employ the process elements common to all as such so that almost no improvements are attained in the dissolving rate and the dissolution efficiency.
The characteristics in the process elements thereof involve:                1) that they are each a tank-type biosolid oxidation method with ozone (being commonly of the tank-type in which aeration is effected by bubbling into a tank);        2) that they are each a method of aeration and oxidation under superlow pressure by utilizing the tank water-depth pressure onto the installation position of the gas disperser unit;        3) that, usually, they are each for aeration with air-dispersion type coarse bubbles of air (ozonated gas) so that the dissolving rate and the dissolution/utilization efficiency of oxygen/ozone are extremely low;        4) that, for the reasons of the above described factors, they are each a process in which a large-size aeration vessel and a large-size reaction vessel are needed;        5) that, for the reasons of the same factors described above, they are each a process with consumption of a large power for the aeration and for ozone generation;        6) that, while it is described that oxidative decomposition treatment of biosolid with ozone is possible by means of an OHR line mixer described later, this is in a stage of mere idea only and has not yet been practiced in the present status because of the limitation in the gas/liquid proportion by the admixture of ozone gas;        7) that the aforementioned mixer which enables formation of ultra-fine bubbles is under a trouble by possible occurrence of blockage by the undissolved solid matter when in a waste water treatment system so that it is understood not to be suitable for application to the aeration step; and        8) that there cannot be found a compact and energy-saving type disposal method enabling high-concentration, high-load waste water treatment and free from occurrence of excessive biosolid.        